Long before the coming of the Imperium, the kingdom of Ultramar was ruled by Roboute Guilliman, the last warrior king of Macragge. Even after learning of his true origins as a primarch, the son of the Emperor of Mankind, he strives to expand the domain of both word and force of the XIII Legion, the Ultramarines, subordinate to him alone. Now, faced with a hostile empire on the world of Thoas, Guilliman must choose his weapons carefully - otherwise his dreams of a brighter future will never come true.